Biomechanics

Comparison of Different Body Postures during Running on Peak Knee and Hip Mechanics

The purpose of the study was to determine whether increasing trunk flexion (TF) and whole body inclination (WBI) angles influences peak knee, hip, and trunk kinematics and kinetics during running. Nineteen participants ran over ground at a self-selected speed under three postures: self-selected normal (SSN), TF, and WBI. Analyses revealed significant differences between conditions for peak knee, hip, and trunk flexion angles and peak knee and hip extension moments. Both TF and WBI postures are effective strategies for reducing peak knee extension moments during running with more load distributed to the hips. This may reduce PFJ stress and therefore aid in knee injury prevention and management. Individual preference of either altered running posture should be utilized in a clinical setting.
Listed In: Biomechanics


Sensitivity to Marker Placement in the TSRHC Foot Model

Multi-segmented foot and ankle (FandA) models provide more information regarding intrinsic foot motion compared to rigid-body models due to additional markers on bony landmarks of the foot. Marker placement sensitivity is a concern, especially in patients with bony abnormalities, because kinematics vary with marker placement deviations. PURPOSE: Assess kinematic changes due to marker placement error using the TSRHC multi-segmented FandA model. METHODS: Our participant was an 18yo female lacking any prior orthopedic conditions. The Plug-in-Gait model was used with the TSRHC model. An experienced clinician executed all marker placements, systematically moving each marker approximately 2.5mm within two planes. Three dynamic trials were collected for each condition, and static trials were used to calculate exact distances markers moved. Six force plates (AMTI) were utilized to confirm a consistent walking pattern. Graphs analyzed included: 1)PIG–ankle dorsiflexion, foot rotation, foot progression angle, 2)TSRHC–hindfoot, forefoot, FF-tibia. For each condition, the peaks of affected kinematic graphs were compared to assess correlations. Intra-trial error was determined by the maximum difference across walking trials. CONCLUSION: The hindfoot was most sensitive to transverse plane marker placement errors. Markers on metatarsals periodically rose vertically when moved laterally due to foot curvature causing errors in the sagittal plane as well. The forefoot also had transverse plane errors when metatarsal markers were moved. This case study illustrates the importance of proper marker placement training when utilizing a multi-segmented foot model. A thorough understanding of a utilized model is imperative, including how sensitive the model is to marker placement.
Listed In: Biomechanics, Gait, Orthopedic Research


Nucleotomy Alters Internal Strain Distribution of the Human Lumbar Intervertebral Disc

Nucleotomy is a surgical procedure following herniation and also simulates the reduced nucleus pulpousus (NP) pressure that occurs with disc degeneration. Internal disc strains are an important factor in disc function, yet it is unclear how internal strains are affected by nucleotomy. Grade II L3-L4 human cadaveric discs (n=6) were analyzed intact and after a partial nucleotomy that removed 30-50% of the NP through a left posterolateral incision (incision) while the contralateral side remained intact (uninjured). Two cycles of stress-relaxation testing were performed for reference (50N) and loaded (0.70MPa) configurations. After each 8hour equilibration period, the reference and loaded discs were imaged separately in a 7T MRI scanner (0.3mm isotropic resolution). The reference and loaded images were registered to calculate internal strain within the annulus fibrosus (AF) lamellae and discs were averaged to create anatomical templates. Circumferential, radial, and axial strains for each disc were transformed to the average templates, effectively normalizing the strains. Five circumferential regions were defined within the mid-third of the templates. Nucleotomy altered disc strains on both the incision and uninjured sides from the intact state. Strain fields were inhomogeneous through the five regions. Mean circumferential strain was unaffected by nucleotomy on the uninjured side, but decreased with incision, showing hoop strains through the AF were disrupted. Mean compressive axial strains were higher after nucleotomy, effectively reducing AF stiffness, and mean radial strains were unaltered after partial nucleotomy. These findings are important to address etiology and progression of degeneration, and to develop and evaluate therapeutic interventions.
Listed In: Biomechanical Engineering, Biomechanics, Orthopedic Research


CROSS VALIDATION OF A FIGURE SKATING BLADE INSTRUMENTED TO MEASURE FIGURE SKATING IMPACT FORCES.

Purpose: To validate an instrumented figure skating blade that is designed to measure impact forces while skating. Methods: Seven subjects (Age: 21.3±2.8 yrs, Ht: 166.9±2.5 cm, Mass: 64.7±7.9 kg) performed 20 landings each onto artificial ice while landing on the instrumented blade from heights of 17.5cm, 25cm, and 33cm. A custom instrumented blade calibrated to measure in forces in Newtons (N) was used to measure impact forces (1000Hz) during landings. These forces were compared to forces obtained while subjects landed on AMTI force plates located underneath the artificial ice surface. Boot angle (250Hz) and force plate data (1000Hz) were collected using Vicon Nexus. Custom LabVIEW programs were used to determine peak force, loading rate, impulse, and the correlation between the blade force data and the force plate data. Paired T-tests were used to compare peak force, loading rate, and impulse between the blade and force plate data. Alpha = 0.05. Results: Correlations between the blade force data and force plate data were good to excellent: mean r (±SD) = .86 ± 0.08. No significant differences were found for peak force and impulse between the blade and force plate data. Peak force means (±SD) were 1353.7 ± 352.2 N for the blade and 1361.2 ± 309.7 N for the force plate (p=.86). Conclusion: The custom instrumented blade is a valid tool for measuring peak forces and impulse during landings. Current research is focused on increasing the gain of the instrumented blade to improve loading rate accuracy.
Listed In: Biomechanics


Movement and Loading Symmetry Changes when Wearing a Functional Knee Brace Following ACL Reconstruction

Asymmetries in discrete measures following anterior cruciate ligament reconstruction (ACL-R) during landing have been reported to be risk factors for secondary ACL injuries. Our purpose was to examine the impact of functional brace wear on kinematic and kinetic inter-limb movement symmetry during landing in ACL-R patients. 20 adolescent athletes (15.8 ± 1.2 years) (7 male, 13 female) 6 months following ACL reconstruction performed 5 trials of a stop-jump task in both a braced (B) and non-braced (NB) condition, with the first landing being analyzed. A custom fit functional knee brace (DJO, Vista, CA) was worn on the ACL reconstructed limb (AL) during the B trials. Mean curves were created for each limb (AL and unaffected limb (UL)) for the vertical (vGRF) and anterior-posterior ground reaction forces (apGRF) and frontal and sagittal knee angles and moments. Coefficients of multiple determination (CMD) between the AL and UL curves were compared between B and NB conditions with students’ t-tests (p≤0.05). No significant differences existed for movement and loading symmetry between B and NB conditions among all subjects. Secondary analysis revealed significant differences in apGRF (p=0.014), vGRF (p=0.011) and sagittal knee angles (p=0.003) in subjects with improved sagittal knee angle symmetry in the B condition. The data show that brace wear improves loading symmetry in adolescent patients that also exhibit improved sagittal knee angle symmetry while braced 6 months following ACL-R. Identifying factors that affect inter-limb movement and loading response to brace wear could assist in determining each patient’s need for a brace.


Listed In: Biomechanics, Sports Science


Ground Reaction Force Symmetry during Sitting and Standing Tasks after a Dual Mobility or Conventional Cup Total Hip Arthroplasty

Dual-mobility (DM) bearing implants reduce the incidence of dislocation following total hip arthroplasty (THA) also it increases hip stability and range of motion (ROM). However, it is unclear whether the improved ROM will lead to better mechanical symmetry. Ground reaction forces (GRF) analysis would help to understand joint compensatory effects and symmetry in THA patients. The purpose was to compare GRF symmetry between the operated and non-operated limbs in THA patients, of either DM or conventional-cup (CC) implant, during standing and sitting tasks. Twenty-four patients and 10 control participants (5M/5F; 62±10 years; 26±4 kg/m2) were recruited and underwent motion analysis before and nine months after THA. Patients were randomly assigned to either a DM (8M/4F; 63±5 years; 28±3 kg/m2) or CC (9M/3F; 62±5 years; 28±5 kg/m2) cementless replacement. Participants performed five sit-to-stand and stand-to-sit trials, with a bench adjusted to their knee heights and each foot on an individual force plate, with motion capture and GRF data been collected. Control group demonstrated standing (0.4±1.6%) and sitting (1.2±1.6%) symmetry. During sit-to-stand, DM group reduced its SI from pre- (5.5±1.6%) to post-op (1.2±1.9%, p=0.09), while the CC group showed a significant improvement (from 8.7±2.1% to 1.5±1.4%, p=0.02). For stand-to-sit, DM group reduced its SI (from 3.3±2.2% to 0.5±1.7%) while the CC group again had a significant improvement (from 8.2±2.1% to 1.2±1.1%, p=0.02). Larger improvements in symmetry were noticed for both groups during trunk flexion when standing; and for CC group during trunk extension when sitting. After surgery, patients with either implant reached SI inside the margin of 1.5 standard deviation from the CTRL (p>0.05). Statistical significance on paired condition was only observed on CC group due to its high pre-op score; however, both surgical groups showed an improved symmetry after THA.
Listed In: Biomechanics, Orthopedic Research


Gait Mechanics Depend Upon Quadriceps Central Activation Ratio in an Anterior Knee Pain Cohort

Gait Mechanics Depend Upon Quadriceps Central Activation Ratio in an Anterior Knee Pain Cohort Son SJ*, Kim HS†, Wiseman B‡, Seeley MK*, Hopkins JT*: *Brigham Young University, Provo, UT, †West Chester University, West Chester, PA, ‡West Virginia University, Morgantown, WV. Context: Quadriceps deficits are often present in an anterior knee pain (AKP) population. However, common self-reported classification tools including Visual Analog Scale (VAS), Kujala Anterior Knee Pain (KAKP), Tampa Scale for Kinesiophobia (TSK), Tegner Activity Level (TAL) scores, and/or other subject inclusion criteria may not be sensitive enough to identify specific movement characteristics in patients with AKP. Quadriceps central activation ratio (CAR) may help to discriminate movement characteristics in patients with AKP. Objective: To examine gait mechanics between two subdivisions of AKP patients, separated by quadriceps function (CAR < 0.95 and CAR > 0.95). AKP patients were defined by VAS, KAKP, TSK, and TAL scores. Design: Cohort. Setting: Controlled laboratory. Patients or Other Participants: 30 (M=16, F=14; 22.3±3 yrs, 175±9 cm, 72.5±14 kg) AKP patients participated: 15 Quadriceps Deficit (QD: CAR = 0.91±0.04, VAS = 3.87±1.3, KAKP = 82.9±6.6, TSK = 37.9±4.7, TAL = 6.3±1.2) and 15 Quadriceps Functional (QF: CAR = 0.97±0.01, VAS = 3.93±0.7, KAKP = 79.3±7.9, TSK = 36.9±5.2, TAL = 6.8±1.4). Interventions: Subjects performed three quadriceps maximum voluntary contractions (MVC) for 3 sec on a Biodex dynamometer (100 Hz). When MVC torque plateaued 1.5-2 sec later, a superimposed burst was transmitted to two electrodes placed on their quadriceps to measure CAR. Two successful trials were averaged for data analysis. Subjects performed five gait trials at a self-selected walking speed. Gait data were collected using high-speed video (240 Hz) and a force plate (1200 Hz). A functional analysis was used to detect mean between-group differences in gait mechanics during the entire stance phase (0-17% = loading response, 18-50% = mid-stance, 51-83% = terminal stance, and 84-100% = pre-swing). This analysis allowed us to compare variables as polynomial functions rather than discrete values. If 95% confidence intervals did not overlap zero, significant differences existed between groups (p < 0.05). Main Outcome Measures: Sagittal-plane knee joint angle (˚), internal knee joint torque (N∙m), and vertical ground reaction force (VGRF; N/kg). Results: Relative to QF patients, QD patients demonstrated (i) decreased knee flexion angle at 4-90% of stance, (ii) reduced internal knee extension torque at 14-32% of stance, and (iii) reduced VGRF at 19-37% of stance and increased VGRF at 46-70% of stance (p < 0.05). Conclusions: The present data suggest that relative to QF patients, QD patients adopt quadriceps weakness gait mechanics that have been reported in individuals with knee osteoarthritis, ACL reconstruction, and effused knee joints. These alterations may create long-term compensatory gait patterns at the knee and adjacent ankle and hip joints, which may lead to mechanical and biological changes in knee articular cartilage. Future research is needed to examine a potential relationship between these gait alterations and articular cartilage health over the long-term.
Listed In: Biomechanics, Gait


Predictors of patellofemoral joint stress: an examination of patellofemoral joint morphology

INTRODUCTION: Patellofemoral pain (PFP) is a common condition seen in orthopedic practice, accounting for approximately 25-40% of all knee injuries [1]. A commonly cited hypothesis as to the cause of PFP is elevated patellofemoral joint (PFJ) stress [2] secondary to abnormal PFJ structure. Previous studies have shown that persons with PFP exhibit altered patella position [3], abnormal femoral morphology [4], and decreased patella cartilage thickness [5] when compared to healthy individuals. However, the influence of the abnormal morphology on PFJ stress is unknown. METHODS: Nineteen subjects (10 PFP and 9 pain-free controls) were recruited for this study. Each subject completed 2 phases of data collection: magnetic resonance imaging (MRI) assessment and biomechanical testing. The measurement of morphological variables (patella height (Insall-Salvati ratio or ISR), lateral trochlear inclination angle (LTI), and patella cartilage thickness). For the biomechanical testing, kinematic, kinetic, and electromyographic were obtained. RESULTS AND DISCUSSION: Pearson correlation coefficients revealed that only patella height (r=0.48, p=0.018) and patella cartilage thickness (r=-0.58, p=0.005) were significantly correlated with peak hydrostatic pressure (Table 1). Results of the stepwise regression analysis revealed that patella cartilage thickness was the single best predictor of peak hydrostatic pressure, followed by patella height. Together, these 2 variables explained 50% of the variance in peak PFJ stress. The results of the current study support the premise that PFJ stress is associated with PFJ morphology. Patella height was the best predictor of PFJ stress with greater degrees of patella height being correlated with greater stress. This is logical given that a higher positioned patella articulates with the more shallow portion of the trochlear groove, thus decreasing PFJ contact area [6]. The finding that patella cartilage thickness was negatively correlated with PFJ stress is in agreement with the results of Li et al. [7], who demonstrated that a reduction of cartilage thickness causes increase cartilage stress. Furthermore, our findings revealed that 50% of the variance in PFJ stress could be explained by morphological factors. CONCLUSIONS: Identifying the underlying factors that contribute to elevated PFJ stress is an important step in developing effective interventions for persons with PFP. Although abnormal structure may not be correctable through conservative measures, it is important to recognize abnormal structure may play a role in contributing to pain and pathology.
Listed In: Biomechanics, Sports Science


Knee Biomechanics of Selected Knee Unfriendly Movement Elements in 42-Form Tai Ji

Tai Ji is one of the recommended non-pharmacologic treatments for knee osteoarthritis (OA), but it is not clear if all Tai Ji movements would be suitable and beneficial for knee OA patients. PURPOSE: To examine knee biomechanical characteristics of the selected knee unfriendly Tai Ji movement elements performed in high-pose position compared to slow walking. METHODS: Seventeen healthy participants (age: 23.9 ± 2.7 years, height: 1.73 ± 0.08 m, body mass: 69.0 ± 13.0 kg) performed three trials in each of the following five test conditions: level walking at 0.8 m/s and four identified knee unfriendly Tai Ji movement elements: lunge, pushdown and kick performed in high-pose position (35 ± 5°) and pseudo-step. Simultaneous collection of 3D kinematics (120 Hz) and ground reaction forces (1200 Hz) was conducted. A one-way ANOVA was performed with post hoc paired samples t-tests to determine differences of the high-pose lunge, pushdown, and kick, and pseudo-step and walking. RESULTS: Knee flexion range of motion for high-pose lunge (29.5°), pushdown (24.3°) and kick (11.1°) was lower than pseudo-step (45.0°, p<0.001 for all comparisons) and walking (47.8°, p<0.001 for all comparisons). Peak knee extensor moment was lower in high-pose lunge (1.04 Nm/kg), pushdown (1.01 Nm/kg) and kick (0.48 Nm/kg) than pseudo-step (1.46 Nm/kg, p<0.001 for all comparisons), but higher than walking (0.38 Nm/kg, p<0.001 for all comparisons) except for kick. Peak knee abduction moment was higher in pseudo-step (-0.61 Nm/kg) than high-pose pushdown (-0.43 Nm/kg), kick (-0.44 Nm/kg), and walking (-0.45 Nm/kg, for all comparisons p<0.001). CONCLUSION: These findings demonstrate higher peak knee extensor moment in most of the Tai Ji knee unfriendly movement elements compared to slow walking. It is recommended that Tai Ji participants with knee OA and other knee pathological conditions modify knee unfriendly movement elements (e.g. lunge) and reduce the size of their movements to minimize knee joint loading. The Tai Ji movement elements including pushdown and pseudo-step should be avoided in the Tai Ji exercises designed for knee OA patients.


Listed In: Biomechanics


IN VIVO ACHILLES TENDON FORCES DURING CYCLING DERIVED FROM 3D ULTRASOUND-BASED MEASURES OF TENDON STRAIN

Introduction and Objectives: Traditional motion analysis provides limited insight into muscle and tendon forces during movement. This study used B-mode ultrasound, in combination with measured joint angles and scaled musculoskeletal models, to provide subject-specific estimates of in vivo Achilles tendon (AT) force. Previous studies have used ultrasound images, tracked in 3D space, to estimate AT strains during walking, running, and jumping [1,2]. Our approach extends this work in one novel way. Specifically, we characterized AT stiffness on a subject-specific basis by recording subjects’ ankle moments and AT strains during a series of isometric tests. We then used these data to estimate AT force during movement from in vivo measurements of tendon strain. To demonstrate this approach, we report AT forces measured during cycling. Cycling offers a unique paradigm for studying AT mechanics. First, because the crank trajectory is constrained, joint angles and muscle-tendon unit (MTU) lengths of the gastrocnemius (MG, LG) and soleus (SOL) are also constrained. By varying crank load, subjects’ ankle moments can be altered without imposing changes in MTU lengths. For this study, 10 competitive cyclists were tested at 4 different crank loads while pedaling at 80 rpm. Based on published EMG recordings (e.g., [3]) and on in vivo tendon force buckle data from one subject [4], we hypothesized that the cyclists’ AT forces would increase systematically with crank load. Methods: We coupled B-mode ultrasound with motion capture, EMG, and pedal forces to estimate in vivo AT forces non-invasively during cycling and during a series of isometric ankle plantarflexion tests. Marker trajectories were tracked using an optical motion capture system. Joint angles and MTU lengths were calculated based on scaled musculoskeletal models [5] using OpenSim [6]. A 50 mm linear-array B-mode ultrasound probe was secured over the distal muscle-tendon junction (MTJ) of the MG and was tracked using rigid-body clusters of LEDs. AT lengths were calculated as the distance from a calcaneus marker to the 3D coordinates of the MG MTJ. Subject-specific AT force-strain curves were obtained from isometric tests using ultrasound to track the MTJ, markers to track both the ultrasound probe and the AT insertion, and a strain gauge to measure the net ankle torques generated by each of the subjects at ankle angles of -10° dorsiflexion, 0°, +10° plantarflexion, and +20° plantarflexion. AT strain during cycling was converted to AT force using each subject’s force-strain relation. Subject-specific tendon slack lengths were calculated as the mean tendon length at 310° over all pedal cycles, based on examination of the AT length changes and on published data showing that this position in the pedal cycle precedes tendon loading across multiple pedalling conditions [4]. Results: Peak AT forces during cycling ranged from 1320 to 2160 N ± 400 N (mean± SD) and increased systematically with load (p<0.001; Fig. 1A/B). At the highest load, the peak AT forces represented, on average, 50 to 70 % of the combined MG, LG, and SOL muscles’ maximum isometric force-generating capacity, as estimated from the muscles’ scaled volumes [7], the muscles’ scaled optimal fiber lengths [5], and a specific tension of 20-30 N/cm2. Peak AT forces occurred midway through the pedaling downstroke, at about 80°, which is consistent with the AT forces directly measured from one subject [4] and with patterns of EMG during cycling [3]. Peak AT strains during cycling were uncoupled from the MG MTU strains and ranged from 3 to 5 % across the different loads examined, measured at the MG MTJ. Conclusion: Our results are consistent with published data from a single subject in which AT force was measured using an implanted tendon buckle [8]; however, our results were obtained non-invasively using ultrasound and motion capture. These methods substantially augment the experimental tools available to study muscle-tendon dynamics during movement. References: [1]Lichtwark and Wilson, 2005, J Exp Biol, 208(24), 4715-4725. [2]Lichtwark et al., 2007, J Biomech, 40(1), 157-164. [3]Wakeling and Horn, 2009, J Neurophysiol, 101(2), 843-854. [4]Gregor et al., 1987, Int J Sports Med, 8(S1), S9-S14. [5]Arnold et al., 2010, Ann Biomed Eng, 38(2), 269-279. [6]Delp et al., 2007, IEEE Trans Bio Med Eng, 54(11), 1940-50. [7]Handsfield et al., 2014, J Biomech, 47(3),631-638. [8]Gregor et al. 1991, J Biomech, 24(5), 287-297
Listed In: Biomechanics, Sports Science